The elements nitrogen (N), phosphorous (P), arsenic (Ar), antimony (Sb) and bismuth (Bi) constitute group 15 or VA of periodic table. Nitrogen is very important and well known element of this group. It constitutes nearly 78.1percent by volume and 75.5 percent by weight of the air is essential constituent of fertilizers, explosives and food stuffs.
After the name of the first element these elements are collectively known as nitrogen family. These elements are also known as pnictogens and their compounds pnictides which contain X3- species. Nitrogen and phosphorus are non metals arsenic and antimony are metalloids and bismuth is a metal.
Nitrogen GroupBack to Top
The nitrogen family elements are listed below.
- Nitrogen (N)
- Phosphorus (P)
- Arsenic (Ar)
- Antimony (Sb)
- Bismuth (Bi)
The nitrogen group was once called the pnictogen group. This comes from the Greek word that means "to choke." The origin of this term comes from the fact that pure nitrogen can cause asphyxiation when breathed in because it does not contain the oxygen necessary to support life.
Nitrogen Family Periodic TableBack to Top
Physical Properties of NitrogenBack to Top
- Physical state - There is a gradual change in physical states of these elements are observed. Nitrogen is a gas, phosphorus is solid and at low temperature it can be vaporized. The other three elements are solids.
- Metallic and non metallic character - Metallic character varies depending on the change in atomic number. Nitrogen and phosphorus are non metals whereas arsenic, antimony and bismuth are metals.
- Allotropy - All elements exhibit allotropy except nitrogen. Phosphorus exists as white, red, scarlet and black phosphorus, arsenic exists in three forms grey, yellow and black, arsenic exists as yellow, black and explosive antimony.
- Melting and boiling points - On moving down the group the melting and boiling points increases with increase in atomic number.
- Density - Density also increases on moving down the group with increase in atomic number.
- Atomic volume, atomic radius and ionic radius - All these property increases with increase in atomic number of the elements of group 15.
- Electronegativity - it decreases on moving down the group indicating a gradual change from non metallic to metallic character.
- Ionization energies - It decreases regularly on moving down the group due to increase in size of the atom and decreasing shielding effect of electrons from the nucleus.
- Oxidation state - it exhibit both positive and negative oxidation state. The common oxidation state is +3. nitrogen shows +1, +2, +4 and +5 and phosphorous shows +4 oxidation state also.
- Catenation - it is shown by all the elements of this group. as is apparent from bond energies the tendency for catenation decreases on moving down the group from nitrogen to bismuth.
Chemical Properties of NitrogenBack to Top
Formation of hydride
Formation of oxides
M + O2 $\rightarrow$ M2O3
Formation of oxyacids
- Orthophosphoric acid - H3PO4
- Pyrophosphoric acid - H4P2O7
- Metaphosphoric acid - HPO3
- Phosphonic acid - H3PO3
- Hypophosphorys acid - H3PO2
- Hypophosphoric acid - H4P2O6
Formation of halides
M + X (halogen) $\rightarrow$ MX3
All the elements of this group form halides of the type MX3. The most stable halides of nitrogen is NF3. Except NF3 and PF3 trihalides are hydrolyzed by water and the ease of hydrolysis decreases down the group. NCl3 is easily hydrolyzed and SbCl3 and BiCl3 are partly hydrolyzed. P and Sb form stable pentahalides but nitrogen do not form pentahalides due to absence of d-orbitals in valence shell. Bi do not form pentahalides due to inert pair effect. PCl5 is used as a chlorinating agent.
HydrazineBack to Top
Hydrazoic acidBack to Top
Free hydrazoic acid can be obtained in high yield from the sodium salt by distillation with dilute sulfuric acid followed by dehydration of the distillate with calcium chloride. Hydrazine can be converted to hydrazoic acid by reaction with nitrous acid in either at 0oC in the presence of sodium methoxide which forms the sodium salt.
HydroxylamineBack to Top
It is used to prepare oximes, an important functional group. It is also an intermediate in biological nitrification. Hydroxyamine is used as a nucleophile in aromatic substitution reactions as a reducing agents and for the conversion of aldehyde to nitriles.
Nitric OxideBack to Top
Nitrous OxideBack to Top
Known as laughing gas because small dose are mildly intoxicating, nitrous oxide is used as a dental anesthetic and as a propellent for dispensing whipped cream.
Uses of NitrogenBack to Top
In particular it may be used to dilute the concentration of a reactant such as oxygen in an oxidation process. In high pressure processes the use of nitrogen permits the use of such pressures while limiting the partial pressure of oxygen.
Nitrogen Family ReactivityBack to Top
Nitrogen is a gas at room temperature. A nitrogen molecule N2 consists of two atoms bonded by a triple covalent bond. Phosphorous on the other hand is very reactive. In general the reactivity increases on going down the group. The trend in reactivity is shown below.
Nitrogen Family CharacteristicsBack to Top
- Atomic radii - Atomic radii of these elements increases in moving down the group.
- Ionization energy - The ionization energy decreases regularly in moving down from nitrogen to bismuth.
- Electronegativity - The electronegativity value decreases on moving down the group from nitrogen to bismuth.
- Melting point and boiling point - Both the properties increases from nitrogen to arsenic due to increase in molecular size.
- Metallic character - On moving down the group metallic group increases.
- Density - This property increases down the group.
Nitrogen Family UsesBack to Top
- Nitrogen is used in fertilizer production and more multiple application of nitrogen fertilizer to obtain more efficient use of nitrogen fertilizer.
- Phosphorus are used for corrosion control in water supply and industrial cooling water systems. Certain organic compounds are used in insecticides.
- The historical use of arsenic were pharmaceutical and medicinal. Arsenic was also commonly used in pigments, poisons and in the manufacturing of glass. A major modern use for arsenic was as pesticides in agriculture.
- Antimony is used in the metallurgy industry, especially in alloys. When it is added to other metals such as lead, it hardens them. It is employed for the manufacture of battery plates and in type metal as well as solders ammunition and electric cable coverings.
- The principle uses for bismuth are in low melting alloys in metallurgical additives for aluminum, carbon steel and malleable iron in pearlescent cosmetic pigments in medicine and in a variety of other smaller specialized applications. The largest single use of bismuth continues to be in the pharmaceutical field.